Separation of mixed metallic sulfids.



L. BRADFORD.

SEPARATION OF MIXED METALLIC SULFIDS,

APPLICATION FILED OCT. 22. 19M- Patented Aug. 6, 1918.

W fl W W UNITED s'rA'rEs PATENT orrIoE.

\i c LESLIE BRADFORD, 0F BROKEN HILL, NEW SOUTH WALES, AUSTRALIA SEPARATION OF MIXED METALLIC SULFIDS.

Specification of Letters mam.

Patented Aug. ,6, 1918.

Application filed October 22, 1914. I Serial No. 868,131.

crude oil and/slimes containing mixed sul-- fids, for the preferential separation of lead sulfid or mixed lead and iron sulfids from applicable also for the treatment of mixed sulfid ores containing values other than lead and zinc.

Heretofore a variety of processes have been suggested for effecting separation of i the exigencies of particular cases lesser extent, ness upon means whlch sulfids from zinc-lead ores by preferential flotation, that is to say, so as to obtain lead sulfid and zinc sulfid more or less separately.

Such processes, however, are to a greater or dependent for their effectivetake advantage of some inherent characteristic of the sulfids by virtue of which they behave distinctively when submitted to flotation treatment. Such characteristic properties of sulfids are not referable within present knowledge to any very definite causes, but they are exhibited markedly in' some ores, such for example as calcitic ores obtained from the Broken Hill mines. It is known that when certain operative conditions are modified to meet in conducting known methods of flotation, such for instance as froth flotation processes, substantially successful preferential flotation of lead sulfid from zinc sulfidis frequently obtainable. These process modifications usually consist in varying the amount and/or the nature of the agitation, or in varying thenature or quantity of the frothing agent employed, or in controlling air supply during agitation. It is also known that 1t 15 possible to exalt the flotation effect in respect of lead sulfid by employing mineral water for or by adding certain mineral salts to the water used in operating the flotation process.

In allthese processes the proportion of the frothing agent used must be controlled wlth care. If excessive amounts of the frothing agent are used, zinc sulfid is floated up with the lead sulfid. Other causes of partial or total failure have been observed.

The present invention consists'in an improved process for effectingithe preferential down with the gangue, but is subsequently separated therefrom by flotation according to known methods.

The process of preferential flotation separation in which my'said invention consists,

is distinguished from known processes by.

the fact that in conducting it the ores orore products containing the valuable "inetallic sulfids to be separated are treated in a medium which wets the zinc sulfid, and which does not wet the lead sulfid and/or pyrites and therefore leaves the last named sulfids floatable while rendering the zinc sulfid temporarily immune to flotation. The lead sulfid and/0r pyrites are thus obtained first as a float concentrate; thereafter the residues comprising gangue and zinc sulfid are treated for the separation of the zinc sulfid from the gangue.

This wetting efi'ect is procured by adding to an acid flotation solution a limited quantity of a substance which is decomposed by said'solution and produces in this decomposition a reducing gas which is more or less soluble in the solution. Notably thiosulfates, sulfites and bisulfites are so decomposed in a solution of sulfuric acid with the production of such a gas (sulfur dioxid). WVith substantially equal result sulfur dioxid may be introduced directly into the solution, either as gas brought into it in a current or added in solution. They like effect is obtained by means of another reducin gas, sulfureted hydrogen, which may be sim arly introduced into the solution or may produced in it by adding sulfids or polysulfids which the solution is capable of decomposlonging to the second group. I indicate in a later part of this specification certaln systematic tests for determining the sultableness and effectiveness of reducing agents for 5 the process. [In carrying out the invention the ore or. ore products ground to a sufficiently fine state of division to suit requirementsare introduced into a return flotation circuit, a small quantity of a suitable reducing agent being first added to the aqueous ore pulp. The pulp isthen submitted to flotation separation, preferably a froth flotation operation in which an organic or other emulslfymg (frothing) agentand acid are added to the aqueoussolution in which the operation is conducted. I find then that the galena and/or pyrites float preferentially and may berecovered substantially by themselyes, while the blende remains temporarily 11 11- mune to flotation because its surface is dium. Having thus preferentially removed the galena and/or pyrites,' the blende may subsequently be recovered from the resldues flotationoperationin a separate circuit of ordinary' character.

Sulfuric acid in practice almost invarialbly used as the acidifying agent in carrying out the process on account of its eflectiveness and cheapness; but an other of the commercial acids will be foun more or less eflective as a' substitute for sulfuric acid.

'Ihequanti-ty of the reducing agent which is required to produce the best efiect varies with the nature of the one, the temperature at which the lead flotation operation is con- 7 ducted, and also, to some extent, on the quantityfof sulfuric acid used in that operation, For these reasons it is not possible to indicate a uniform rule to govern the correct quantity of reducing agent to be fid. 3 That qu'aggtity must be determined in k u ea h case by l oratory tests.- Ordinarily from 8 one. toS lbs. of reducing agent per ton ofpre to be treated will be found sulficient-for the purpose of my invention, but I do not bind myself strictly tmthese limits of proportions. Theaddition of an execs-- j sive quantity of reducing ent has a bad 65. efiect-, .in that the preferential flotation of wetted by the active reducing flotation me- 1n any known manner as a high grade zinc concentrate substantially free from galena 'reducing agent into the flotation medium,

whereby it is caused to be wetted, varies more or less directly with the proportion of the wetting agent in the flotation medium.

By varying the proportion of the wetting agent used,.-the flotation of the blende can on the one hand be entirely prevented or substantially so, or on the other hand the blende may be only rendered temporarily immune to flotation for a limited time. A proportion is determined which has the eflect of immunizing the zinc sulfid for a suflicien-t time to enable a satisfactory recovery of the galena contained in the ore prior to submitting the deleaded zincky residue to further flotation for the recovery of the blende.-

The process is suitable for the preferential flotation and recovery of galena from coarsely crushed ores as well as from slimes; and is applicable to the treatment of any ore admixture containing galena and/or pyrites and blende irrespective of the pro portion of grit and slimes present,so long as the ore particles are of floatable size and have not been subjected to preceding treatment which would render the reducing agent inoperative for the wetting of the zinc sulfid or render the lead sulfid and/or galena non-floatable.

In the actual application of my invention to a Broken Hill mixed sulfid containing zinc and lead sulfids, I conduct the flotation operation inan apparatus such as that shown in sectional elevation in the accompanying drawing. In this drawing a is a for slowly revolving the shaft 6' so the contents of the tanka will be mixed into the condition of a -freely flowing pulp. Into this tank or box a the pulverized ore and solution are delivered. Near the bottom of the said mixer box a is fixed-an exit pipe c with a valve togregulate the flow of the I pulp to a centrifugal-pump g which in this case is used as an agitator. The runner shaft of the pump glmay be driven by the puley g: and supported in bearings 9 The inta pipe It to the pumphas a small pipe z fixed in it for the addition of sulfuric acid in any required (plantity. A steam air injector k is tapped into the barrel of the pump g'for the dual purpose of heating the ore pulp, and for'the introduction of atomized air if found'necessary. The exit pipe 1 from the centrifu al pump is pro vided with a valve m or regulating or throttling the delivery of the agitated pulp in any quantity. The thoroughly gassed pulp is deliveredby the pumpjg under pressure into a spitzkasten n,-where the separation takes place; the sulfids floatto the top, and are allowed to flow away as concentrates by chute 0 while the residues sink to the bottom and escape through a continuously running lug hole 1). It will be readily understood that the requisite quantity of reagents" can be delivered by gravitation or otherwise into the intake pipe h to effect the reaction needed in the process and also that .the steam and air entering in adjustable quantities will respectively heat and aerate the pulpy mixture to assist the separation aimed at.

In operation the centrifugal pump fulfils the dual function of churning and delivering the pulpy mixture, the stop valves being so adjusted that the throttling by the valve 111. will cause the pulpy liquid to be frothed or aerated by the runner of the pump.

The flotation boxes are set in series and the rate of treatment about 25 tons per hour.

No serious difficulty is experienced in correctly proportioning the sodium thiosulfate used (theblende wetting agent) so as to insure the rapid floating oil of the galena substantially pure or as a high grade concentrate rich in silver, and to leave the residue in a condition suitable for further flotation treatment for the recovery of the zinc sulfid therefrom.

The flotation treatment is preferably conducted according to the froth flotation principle; the procuring of the effect aimed at is dependent upon the presence of a frothing agent in the flotationmedium, only when a reducing gas is introduced into the medium; it is not dependent upon the presence' of a frothing agent in, the flotation medium when a reducing gas is generated in the flotation medium by reaction of a substance introduced intojt. In some cases I findv that-enhanced results are obtained digesting the ore with sulfuric acid and the re ucingagent in a thick pulp prior to 'subjecting the same to a flotationoperation.

By way of example of the working of this process the followingtest results are quoted.

(1) 500 grams of a weathered Broken Hill dump slime containing zinc 18.2%, lead 15.2%, oxidized lead 4.0%, silver 18.3 ozs. per ton, were introduced into an agitation flotation machine with Baliters cold water; 1 gram of sodium .thiosulfate was first added, and then 5 c. c. of sulfuric acid. This amount of acid was sufli'cient to render the concentrate r1 9.6%, lead 60%, oxidized lead 2.3%, and

A frothing agent by this means silver 69 ozs. per ton. After the galena has 7 been so recovered, 0.1 gram of potassium permanganate was added to neutralize the reducing 'characterof the medium, andthe blende was then floated, the recovered product yielding 166.5 grams of a good grade zinc concentrate, assaying zinc 46.4%, lead 6.3%, oxidized lead 1.6%, silver 15.7 ozs. per ton. The tailings resulting from this treat- .ment weighed 238 grams, and assayed zinc 2.0%, lead 7.2%, oxidized lead 6.2%, silver 3.7 ozs. per ton. These operations were carried out in normal atmospheric temperatures.

(2) 500 grams of a Broken Hill ore containing zinc 15.5%, lead.11.0%, silver 9.9 ozs. per ton was crushed in a tube mill to a floatable size. The crushed ore consisting of grit and slimes admixed was treated as in the previous test, 0.5 gram of sodium thiosulfate being used, and the operation conducted at a temperature of 100- F. The float of 61 grams of lead concentrates recovered assayed zinc 10.6%, lead 62.8%, silver 35.8 ozs. per ton. After the lead sulfid had been thus preferentially floated, the agi 'tation was continued for a time and a little more acid and frothing agent were added,

and 125.5 grams of Z1110 concentrates were floated. This product assayed, zinc 48.6%, lead 5.8%, silver 15.4 ozs. per ton. The tailings weighed 298.5 grams and assayed zinc 2.8%, lead 2.7%, and silver 2.5 ozs. per

was then transferred from the flotation machine to a bucket in which the ore was allowed to settle. The supernatant liquor was then decanted, and the ore was-reintroduced into the machine, and the blende .was floated in hot water to which more frothing'agent was added. The zinc concentrates thus floated weighed 220 grams, and assayed zinc 51.6%. The residual tailingsweighed 120 grams, and assayed zins 3.7%.

(4) 500 grams of a Tasmanian ore contaimng a mixture of "galena, pyrite, and

v blende, assaying zinc 28.5%, lead 8.2%, silof a frothing agent were added. 148-grams of pyritic concentrates floated preferentially; these assayed 13.4% zinc. The pulp ver 9.5 ozs. per ton, were introduced into a 1000 c. c. stoppered cylinder with 500 c. 0, hot water; sulfuric acid was added in suficient'quantity to render the ore pulp slightly acid; and then 2 grams of sodium sulfite -'were introduced, and the mass was agitated few crystals of potassium permanganate,-

and a few drops of eucalyptus oil being added. This produceda flotation of -210 grams of zinc concentrates,- amying zinc 53.2%,

- lead 6.0%, silver4=.0 ozs. The tailings weighed 75 grams and assayed zinc lead 1.0%,silver 1.0 ozs. per ton.- Y I I have not determined 11 thereducing agents other than sodium thiosulfate and sulfurous acid and sulfurated hydrogen and alkaline sulfites and bisulfiteswhich will operate at suitable bende wetting agents or media foreflectihg the purpose of this invention. The following described laboraf tory tests will however satisfactorily determine the efficacy for such purpose of any substancehaving reducing action I Take 100 grams of the ore to be concentrated in a finely crushed condition; Transfer this ore into a 500 c; c. stoppered' cylin der with water. Introduce the fwett-ing agent to be tried out, and agitate. Then add suflicient sulfuric acid to render the whole slightly acid.' Add a small quantity of a frothing agent, such as eucalyptus oil, and agitate violently for from two to five minutes. Then critically inspect the contents of the cylinder. If the blende w'et ting agent. employed in the particular testis found to leave the blende particles free and non-granulated, and at the same time permits the galena and/or pyrites particles V to granulate or coalesce together, it is an indication that that wetting agent will be found suitable for the treatment'of that the blende particles on the one hand con:

' sidered as a group and the galena and/or .pyrites particles on the other hand considered as a separate group, repeat the test with a practical maximum quantity of the proposed blende wetting agent, and notethe diflerence in behavior of the zinc sulfid from the other sulfids present. 7

To determine the proper quantity of any particular reducing (blends wetting) agent to .be used for the purpose of this incontaining sulfur.

masses vention to yield the most eflective result, and also to ascertain the degree of temperature best suited in particular cases,\act,ual flotation separations must be made on a labora.- tory scale by first floating the galena and/or pyrites with acidu'lated solutions containing a predetermined test proportion of the reducing reagent, then draining the remainder of the ore, floating the blende' therefrom by dinown jflotatiori methods,- and assaying the floated products in the usual manner. Repetitions of thisstestma y be madethrough a range of temperatures and with various per centage's of blende wetting agent in the first-flotation medium.

The particular operative apparatus and manipulations usable for carrying'out any flotation operating bymeans of my herein i -'described process and practically effecting thereby flotation of galena and/or pyrite, 'are not elements or my invention, and I make no claim upon same; My invention may be successfully carried out by following any well knownvmethods of separating ore products by flotation in. known apparatus, and it involves, qua flotation apparatusand operations 'no novelty.

at I claim as my invention and desire to secure by Letters Patent is 1. Thenproces for treating, zinc sulfid -(blende) ores for the separation of lead sulfid (galena) and pyrite therefrom, which consists in submitting such ores in amore; or less finely divided condition to flotation treatment in a separating medium Which-does. not chemically or otherwise permanently aflect any of the particles, but does act: upon-the surfaces of said zinc sulfid (blende) particles by wetting them but without similarly wetting the sulfids mixed therewith, whereby the said zinc sulfid (blende) particles are caused to sink while the remaining sulfide are permitted to float; said separating medium being acidulated water containing in solution a reducing gas 2. The process for separating zinc sulfid (blende) from admixture with other sulfids such as lead sulfid (galena) and iron sulfids (pyrite), which consists in introducing such sulfid mixture in more or less finely divided condition into an 'acidulated liquid containing in solution a reducing gas. containing sulfur and subjecting the mixture to flotation. treatment, whereby said zinc sulfid (blende) particles are 7 wetted and caused to sink and the remaining sulfids permitted to float, decanting said floating sul'-' fids. and afterward reclaimlng said zinc sulfid (blende) 3. The'process of separating thesulfids of zinc, lead, and iron by selective flotation,

the mixed which consists in introducin sulfids' into a floating liquid and impregnatblereducing gas'containing sulfur in quantity suflicient to cause wetting of the sulfid of zincwithout aflecting the sulfid of lead. 5 it-The process ofseparating the sulfids 5 of-zinc (blende) from the. sulfid of lead (galena) and iron (pyrite) which comprises the step of introducing the comminuted sulfids into a frothing liquid containing a partially soluble'sulfurous reducing gas, there causingthe wetting, of the blende without aiiecting the galena and without causing permanent change on either;

5. The process of separating zinc sulfid (blende) from the sulfids of lead-(galena) and iron (pyrite), which consists in submitting such ores in a more or less finely divided condition to flotation in a separating me- 'dium which does not chemically or other-, wise ermanently affect the zinc sulfid (blend e) particles, 'but' does act upon the surfaces of said zinc sulfid (blende) par ticles by wetting them, whereby the said 4 zinc sulfid (blende) particles are caused to sink'while the remaining sulfid particles are permitted to float, said separating medium being Water containing a frothing K agent and a soluble reducing gas containing sulfur. I '5'. v v 6. The process for separating zinc sulfid '30 (blende) from admixture with other sulfidssuch aslead sulfid (galena) and,iron sulfids (pyrite), which consists in introducing suchsulfid mixture in more or less finely divided condition into an aqueous liquid containing a frot ing agent and a slightly soluble, sulfur-c ntaining, reducing gas, whereby .the zinc sulfid (blende) particles 'are wetted and caused to sink, frothing the liquid, removing the froth-borne sulfids, and

40 separately recovering the deposited zinc sulfid or blende.

7 In the process of separating the sulfids of zinc, lead, and iron b selective flotation, the step' which consists in fr'othing the sulfids in an aqueous liquid containing in solution a reducing gas containing sulfur thereby causin the wetting of the sulfid of zinc without'a ecting the sulfid of lead and without causing chemical change on either. 8. The process for treating zinc sulfid (blende) ores for the separation of lead sulfid (galena) and pyrite therefrom, which consist in submitting such ores to flotation in a more or less finely divided condition ina separating medium which does not chemically or otherwise permanently affect any of the particles, but does act upon the surfaces of said zincsulfid (blende) particles by wetting them but without similarly wetting the sulfids; mixed therewith, whereby the said zinc sulfid (blende) particles are caused to sink while the remaining sulfids are permitted to float; said separating medium bein water acidulated with sulfuric acid and a ounding in sulfur dioxid.

9. The recess of separating the sulfids of zinc, lea and iron by selective flotation which comprises the steps of impregnating the floating liquid with sulfurdioxid, introducing the mixed sulfids therein, and subjecting them to thereby causin the wetting of the sulfid of zinc without a ecting the other sulfids.

-10. The process of separating the sulfids of zinc, lead and iron by selective flotation which comprises the steps of acidulating water with sulfuric acid, adding thereto a substance that will react therewith to evolve sulfur dioxid introducing the sulfids in the medium thus formed as a floating liquid, and subjecti g the mixed sulfids to flotation treatment erein, said sulfid of 'zinc being thereby wetted and temporarilyjrendered immune to flotation without sulfid of lead.

11. The process of separating the fulfid of zinc (blende) from the sulfids of lead (galena) and iron (pyrite) which comprises affecting the the step of introducing the comminuted sulfids into a frothing liquid containing an acid and a substance that will react with such acid to evolve asulfur-containing reducing gas, and submitting said mixed, sulfids to flotation treatment therein, said reducing medium causing the wetting'of the sulfid of zinc without affecting the sulfid of lead.

12. The process of separating blende from galena and pyrite contained in mixed sulfid ores, which consists in submitting said ores in a finely divided condition to flotation separation in a medium consisting of a dilute aqueous solution of sulfurous acid, said medium causing the wetting of thesulfid of zinc and rendering the same temporarily immune to flotation, agitating the mass and removing the float and sedimentary deposit separately.

13. The recess of recovering zinc sulfid (blende) rom an ore comprising blende, galen'a, pyrite, and gangue which consists of submitting the comminuted ore to flotation treatment in an acidulated, aqueous eleflotation treatment therein,-

ment containing a sulfurous reducing gas,

whereby the blende vand gangue w1l1 be caused to sink and the remaining sulfids to float, and thereafter neutralizing the reducing character and repeating the) flotation whereby the blende may be caused to float .and the gangue alone to settle.

14. In the process of recovering blende from a compound sulfid ore containing iron, lead, and gangue by the successive flotation method, the steps which consist in first submitting the comminuted ore to flotation treatment in a floating liquid containing a sulfurous reducing gas, whereby the .blende and gangue are wette and caused to sink, then adding a chemica to neutralize the blende wetting character of the liquid, and finally repeating the floating operation,

whereby the blende is floated away and the gangue deposited. v

15. The process of recovering zinc. sulfid (blende) from an orecomprising 'blende,"

liquid along with a sulfur-containing chemical of a nature to react with said liquid to 1 produce a soluble, sulfurous, reducing gas,

recovering separately the floating and sedimenting parts of the ore, and repeating the flotation of the sedimenting parts with the use of non-reducing liquid.

16. The process of. flotation consisting in treating ore containing lead and. zinc sulfids to divest the zincsulfid particles of the gaseous envelop aboutthe same, without otherwise altering said zinc sulfid particles, and without removing the envelops of other sulfids, and subjecting the so treated ore to flo- 'tationu 17. The process of flotation consisting in so treating ore pulp containing zinc and lead 25 sulfids as toalter the physical conditions atv the surfaces of the zinc sulfid particles to render the same immune to the normal adhesion of flotative agents, without chemical ,alteration of said surface and without similarlyafi'ecting the other sulfids, and subject-- ing the so treated pulp to flotation.

18. The process of, separation consisting in delivering ore containing mixed sulfids to an acidulated bath containing in solution a reducing gas containing sulfur in quantity suflicient to cause wetting of one sulfid without affecting another and without causingv to an acidulated bath containing in solution a reducing gas containing sulfur in quantity sufiicient to cause wetting of one sulfid with-- out aflecting another and Without causing chemical change on either, and subjecting the mixture to flotation to float the unafl'ect'-' change on either sulfid, and subJecting the mixture to flotation to float the unaifected' sulfid. g

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses. LESLIE, BRADFORD. Witnesses g p I WILLIAM BURBON nsHALL, An'rmmJAMEs Larson. 7 

